This study examines how two distinct patterns of online political information exposure—pro-attitudinal selective exposure and counter-attitudinal incidental exposure—can work together to influence engagement in online cross-cutting political discussion. Using panel data from a two-wave national survey conducted in 2012, we test two competing theoretical accounts. Findings suggest that incidental exposure affects selective exposure’s contribution to cross-cutting discussion in a curvilinear way. Incidental exposure strengthens the impact of selective exposure on cross-cutting discussion up until a certain point, after which it begins to attenuate its impact. Results emphasize the need to account for the multiple ways people encounter political information online.